1. Field of the Invention
The present invention relates to a polarizing element typified by a polarizing plate, polarizing filter, or the like, and a method for the polarizing element.
2. Description of the Related Art
In liquid crystal displays, particularly transmissive liquid crystal display devices, based on the principle of image formation, it is essential to dispose a polarizing plate on a surface of a liquid crystal panel. In recent years, development of liquid crystal displays being miniaturized and having high-luminance has been promoted, and polarizing plates having high heat-resistance and high light-resistance have been needed accordingly. For example, in the case of liquid crystal displays in which a light source having a large quantity of light, such as a transmissive type liquid crystal projector, is used, a polarizing plate receives a strong radiant ray. Accordingly, excellent heat-resistance is needed for the polarizing plate used for these liquid crystal displays.
Conventional polarizing plates using an organic film have insufficient heat-resistance and light-resistance, and, due to a strong radiant heat from a high-luminance light source, remarkable deterioration of the polarization characteristics has been observed. On the other hand, a wire grid type polarizing plate including a metal fine grid has been proposed. The wire grid type polarizing plate is configured such that a plurality of metal thin lines are formed in grid-like fashion on a substrate, wherein a polarization component parallel to the metal thin lines is absorbed or reflected while a polarization component perpendicular to the metal thin lines is transmitted, whereby predetermined polarization characteristics appear.
A metal fine grid is obtained in such a manner that a metal film, such as aluminum, is deposited on a substrate by sputtering, evaporation, or the like, and a high-density fine resist pattern is formed on this metal film by photo lithography, such as interference exposure. However, at the time of the exposure of the high-density fine resist pattern, a reflective interference light from a surface of the metal film generates, thereby making the resist pattern shape not a simple rectangular shape but a shape whose width is locally constricted with respect to the height direction. As a countermeasure against this, a bottom anti-reflection coating (BARC) is applied under a resist layer to reduce the constricted portion. However, it is not possible to prevent occurrence of the constricted portion completely.
When the constricted portion appears in the resist pattern, the resist pattern easily falls, and the pattern falling prevents resolution, and thus leads to degradation of resolution characteristics. In other words, when a resist pattern falls, the resist pattern cannot become a processing mask at all, whereby desired polarization characteristics cannot be achieved.
Furthermore, a constricted portion in a resist pattern causes not only a pattern falling problem, but also, in the case where the resist pattern is used as a mask for dry etching, causes process instability, such as variation in etching rate, whereby productivity is worsened and manufacturing cost becomes higher.
As a solution to such problems, there has been proposed a polarizing element which is obtained in such a manner that a pattern formation layer is provided on a substrate transparent to visible light by using a material transparent to visible light, such as SiO2, to form a grid-like projection and depression portion, and then an inorganic fine particle layer made of an aluminum material or a semiconductor material is provided in a top portion or at least one side portion of said projection and depression portion from a direction oblique with respect to a surface of a substrate. (Refer to Japanese Patent Application Laid-Open No. 2007-148344). In this polarizing plate, a projection and depression portion having a texture structure is formed by lapping or rubbing using a polishing sheet, or by die transcription, whereby, without pattern etching, an inorganic fine particle layer having a desired fine shape can be formed.
However, depending on a shape of the projection and depression portion, as shown in FIG. 8, when metal fine particles 51 are made to adhere from a direction oblique with respect to a surface of a substrate 50, the metal fine particles 51 protrude over a space 53 between a projection portion 52 and a depression portion 52, whereby a transmissivity of light L is decreased. This tendency becomes remarkable as a grid pattern is made finer. For polarizing elements, transmissivity is an important factor as well as contrast in the evaluation of the characteristics, and accordingly, there is desired a polarizing element in which a desired grid pattern is formed and also a transmissivity is not lost.
The present invention has been made in view of the above-mentioned problems, and aims at providing a polarizing element having desired polarization characteristics in a visible light region and a good light transmissivity, and a method for manufacturing the polarizing element.